The invention relates to a method of forming a high temperature resistant copper coating on an inorganic dielectric, preferably ceramic and enamel substrates, by means of chemical or galvanic metal deposition. Methods of forming a copper coating on inorganic dielectrics by means of chemical or galvanic metal deposition are generally known.
Copper coated base materials such as ceramics and enamel coated metal bases, are used for producing electronic circuits and, preferably, for circuits which among others are used where a high heat conductivity is required or where they are subjected to elevated working temperatures.
The function of a high-energy substrate in electronics is to permit flow of a very high current through conducting paths. They also should enable rapid dissipation of heat losses from structural elements. Powerful semiconductors having a commutation current of about 100 A to this effect should be brased to such metallized substrates. A ceramic substrate having a copper coating or a copper coated enamel substrate having a metal core perform this dissipation better than lattice substrates with raised and firefixed thick layer of a conductive paste, because the thermal and electrical conductivity of pure copper is significantly better.
The drawback consists, however, in that the load-carrying capacity of the structural elements: substrate, chemically deposited copper--galvanically deposited copper is limited by a maximum temperature of 290.degree. and, beside, can be kept at that temperature no more than about 10 min.
At higher temperatures or a longer thermal load, impurities contained therein such as especially liquid remnants, cause destruction of element connections as a result of formation of blowholes in metal coatings.